1. Field of the Invention
The present invention relates to a method of manufacturing a semiconductor wafer wherein the back surface of a starting semiconductor wafer which is formed with a plurality of semiconductor chips, for example, ICs or LSIs, in its front surface is equally ground and thinned all over by a grinding apparatus, and an oxide film or the like is thereafter formed on the ground back surface.
2. Related Art
A semiconductor wafer of the type specified above, formed with a plurality of semiconductor chips such as ICs or LSIs, has its back surface ground and thinned by a grinding apparatus, and the ground semiconductor wafer is thereafter split into the individual semiconductor chips by a splitting apparatus such as dicing apparatus. The semiconductor chips are assembled and extensively utilized in the circuits of electric equipments such as portable telephones and personal computers.
Meanwhile, as the structures of semiconductor chips have been thinned in recent years, laminated chips in each of which semiconductor chips are vertically stacked to enhance functions, processability, a storage capacity, etc. have been put into practical use. Thus, it permits to make electric equipments, such as portable telephones and notebook type personal computers, thin in structure, small in size and light in weight.
In the manufacture of the laminated chips, at the stage of a semiconductor wafer, electrodes extending from the front surface of the semiconductor wafer formed with circuits to the back surface thereof are embedded, and they are exposed by subjecting the back surface to mechanical grinding or chemical etching. In addition, an insulating film such as SiO film is formed on the back surface of the semiconductor wafer in order to prevent copper or other metals forming the electrodes from diffusing into a semiconductor such as silicon.
Also a technique is put to practical use wherein, after the circuits of power transistors etc. have been formed in the front surface of a starting semiconductor wafer, the back surface of the semiconductor wafer is ground or etched, a metal film of titanium (Ti), silver (Ag), gold (Au) or the like is formed on the worked back surface to a thickness of several tens nm, thereby to construct a semiconductor wafer.
In such a case where the back surface of the semiconductor wafer formed with the circuits in the front surface is thinned by grinding, polishing or the like, and where the film is thereafter formed on the back surface, the semiconductor wafer needs to be formed as thin as possible, for the purpose of making the thermal and electrical characteristics of the semiconductor chips favorable.
However, when the semiconductor wafer is thinned and worked to a thickness of, for example, about 100 μm–15 μm, there is the problem that the semiconductor wafer is warped to hinder the formation of the film, so the film cannot be uniformly formed.
Especially, when the film formation is carried out by a reduced-pressure film formation apparatus to form the film in a reduced-pressure environment, a suction force cannot be used in a holding table for holding the semiconductor wafer, and the semiconductor wafer is held by an electrostatic scheme. Therefore, the stress of the film resists the holding force of the holding table based on the electrostatic scheme and warps the semiconductor wafer, and the film cannot be uniformly formed.
In the present situation, accordingly, the thickness of the semiconductor wafer is limited to about 200 μm in order to bestow enough rigidity to prevent the warp, and the semiconductor wafer cannot be formed to be thinner (refer to JP-A-2001-93863).
In order to realize the formation of a uniform film even when the semiconductor wafer is formed to be thinner in the case where the film is formed on the back surface of the semiconductor wafer, the inventor has developed a technique wherein the semiconductor wafer is stuck and supported on a support baseplate of high rigidity, such as glass baseplate, the semiconductor wafer has its back surface ground so as to be thinned to a required thickness in that state, and the required film is thereafter formed on the back surface of the semiconductor wafer by a film formation apparatus. The technique has already been applied for a patent under the name of the same assignee as that of the present application (refer to JP-A-2004079889).
In this regard, however, a problem has been revealed as stated below. When the back surface of the semiconductor wafer is ground by a grinding apparatus, contaminants having appeared during a grinding work step adhere to the back surface of the support baseplate, and the semiconductor wafer is thereafter subjected to a cleaning step. Herein, the adherent contaminants cannot be completely removed at the cleaning step. When the semiconductor wafer is transported into the film formation apparatus and is formed with the film under a reduced pressure, there occurs a problem that the contaminants not having been removed pollute the interior of the film formation apparatus, to degrade the quality of part of the film formed on the back surface of the semiconductor wafer.